Publishing Fault to FTP service?

When publishing I enter all the correct data:

server address

user name

password

Directory/Path (Blank)

Protocol: FTP

Then I test connection and all ok.

HOWEVER nor my hoster tell me I need to Add in Directory/Path: /public_html

Then I get an ERROR MESSAGE:

The Directory/path could not be found. Verify your settings and try again..

What am I doing wrong?